Space current device



Oct. 24, 1933. W. J. K|MME| 1,932,077

SPACE CURRENT DEVICE Filed Feb. 15, 1930 INVENTOR AT'ToRN EY Patentes oet. 24, 193s PATENT OFFICE SPACE CURRENT DEVICE William J. Kimmell, Trafford, Pa., assignor to Westinghouse Electric & Manufacturing Company, a corporation of Pennsylvania Application February 15, 1930. Serial No. 428,637

3 Claims.

This invention relates` to space current devices and more particularly to an alternating current heater for a uni-potential cathode.

One object of the invention is to provide a 5 coiled electric heater that will be substantially self-neutralizing in regard to its magnetic field.

Another object of the invention is to provide a heater for thermionic tubes that will require no additional supporting member between its ends.

More specically stated it is an object of this invention to provide a heater of a substantially hairpin shape having coils on one leg of the heater interspersing the coils on the other leg,

the heater being coated with an insulating refractory material.v

lt has'hereto been customary in constructing an alternating current heater` for the equi-potential cathode of vacuum tubes to form the heater into a substantially hairpin shape with more or less straight sides so that the electromagnetic field of one side will neutralize that of the other, and so prevent hum. This usual shape of the heater has the disadvantage that the length of the wire used is rather limited to a definite amount by the adoption of a standard size of tube. Furthermore, the rangel of materials suitable for a heater is also very limited. As the temperature relation between the heater and the cathode is more or less determined by the length, the crosssection, and resistivity of the heater for a given current voltage, this shape of heater does not provide a flexible enough design for changing the amount of heat produced. This is due to the fact that the length of resistivity is generally fixed.

On the other hand, where the length of the heater has been increased by the use of some other shape than that of the straight hairpin, there has usually resulted an unneutralized magnetic field that is apt to produce hum in the loud speaker or to otherwise disturb the circuit.

This invention contemplates providing a heater in which the length of the heater can be chosen in regard to the desired temperature to be produced in the cathode, and, at the same time, have the Various portions of the heater substantially neutralize the magnetic effect produced by other portions of the heater.

Another disadvantage of the prior heater art has been the type of support usually provided. In some cases, a separate support extends to the middle portion of the wire, requiring careful A land hence more expensive manufacture. If on the other hand, a mass of material, large in com- (Cl. Z50-27.5)

parison to the size of the heater is attached to the cathode to support a heater within the cathode, this mass absorbed a portion of the heat produced by the heater and accordingly has extended the time for the equipotential cathode to reach an operating temperature. y

It is an object of this invention to coat the heater with astiiening insulating coating so that the heater is not apt to be vibrated. Furthermore..on account of the coating being an insulation, the heater may accidentally or designedly make physical contact without electrical contact with the equipotential cathode. Thus addi# tional supporting means are not necessary.

Other objects of my invention will become evident from the following detailed description taken in conjunction with the accompanying drawing, in which:

Figure 1 is a view partly in elevation and partly in cross-section of a thermionic vacuum tube to which the invention has been applied;

Fig. 42 is an elevation of the heater after the first preferred step in its formation;

Fig. 3 is an elevation of the heater after it has been formed into its final preferred shape; Fig. 4 is a cross-section through the completed heater element.

Fig. 5 is an elevation of a preferred form of heater of less effective length than that of Fig. 3.

The apparatus shown in Fig. 1 is a thermionic 85 tube with the hollow glass bulb 10 and the insu. lating base 11. The press 12 is supported within the tube and has sealed therethrough a plurality of connections 13 for the inner elements of the tube. In the interior of the tube is an alternating current heater 14 surrounded by an equi-potential cathode 15, preferably in the shape of a hollow cylinder. Surrounding this cathode and spaced therefrom is the grid 16. An anode 17 also preferably surrounds the grid, cathode, and heater just described. Each of these elements has suit.- able connections through'the base of the plug as shown in the drawing. Y

It will be noted that the preferred form of the heater 14 is substantially a hairpin shape, but, 100 instead of having the ordinary straight sides, each side or leg, or portion has a plurality of loops 18,

19 extending more or less laterally towards the other side or leg, or portion of the hairpin heater.

While any suitable spacing between the two v the current passes through the heater, but as one v rection of the current in one portion is in the opposite direction to the current in the other portion and the magnetic eld produced by one portion is accordingly opposite in direction to the magnetic field produced by the other portion. The proximity of the coils 18 of one portion to the coils 19 on the other portion, will naturally result inthe magnetic field produced by the coils 18 of one portion being neutralized by the opposing magnetic eld produced by the coils 19 of the other portion. In other words, in regard to the heater and, accordingly, the amount of heat produced, varied in proportion for a given current. If a wire of less effective length is required than that of Figs. 1 and 3, a fewer number of loops may be made as in Fig. 5. As disclosed in this gure it is preferred to closely couple acoil 18 on one leg of the hairpin With a coil 19 on the other leg of the hairpin. The pairing of coils substantially neutralizes the magnetic eld that would normally be produced by eachcoil.

A preferred form of shaping the heater is illustrated in Figs. 2 and 3. A wire, preferably of tungsten, is coiled as disclosed in Fig. 2. This wire is then preferably stretched to space the coils still more, and a portion is then preferably turned back upon the other portion as illustrated in Fig. 3 so that the coils 19 on the second portion intersperse the coils 18 on the rst portion of the heater. The ends of the heater are then preferably sealed in a glass press such as 12, disclosed in Fig. 1, and the heater is then coated with an insulating coating.

It is preferred to use a stiffening and insulating refractory coating for this heater sozthat the usual support for the center portion of the heater may be dispensed with. This refractory coating is preferably formed of alumina (A1203). This insulating refractory coating may either be sprayed on by a spray gun and baked, or it may be deposited electrolytically. The alumina and a binder, which may include a less refractory clay like kaolin, may be sprayed on the heater and then baked with the result that the hydro-carbon binder is burned off leaving a porcelain refractory coating on the heater. In case the coating is put on electrolytically, the electrolyte may be composed of 90% alumina with the remaining portionvcomposed of kaolin mixed with water and ammonium hydroxide. The result is disclosed in Fig. 4 which is a cross-section through the comportion is bent back on the other portion the dipleted heater, and discloses the original tungsten Wire 20 surrounded by the insulating refractory coating 21.

An examination of Fig. 1 will disclose that no special support is provided for the heater between its ends. The coating 21 stiffens the heater. The insulating properties of the coating however, permit the heater to make physical Contact Without electrical contact either accidentally or designedly with the interior of the cathode l5. As no additional support is required for the heater in Fig. l, the heater is self supporting in this arrangement;

The self-supporting type of heater is not only simpler to manufacture, but it also dispenses `with the usual mass of material used to support the heater and which would normally absorb an additional amount of initial heat and would accordingly increase the time for the cathode to reach operating temperature.

This refractory coating, which is more specilically porcelain, also reduces the hum that would normally be due to `electrostatic effects between the heater and the cathode.

Accordingly, there has been disclosed that an alternating current heater for an equi-potential cathode in which the effective length of the heater can be selected as desired, and which is substantially self-neutralizing in regard to its magnetic field. Furthermore, this heater is selfsupporting in its preferred use which makes it not only simpler to manufacture, but also dispenses with the ordinary mass o-f heat absorbingmaterial used to support it inside the equi-potential cathode.

Although I have vshown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except as is necessitated by the prior art and by the scope of the appended claims.

I claim as my invention:

1. The method ofmaking an electric heater for thermionic tubes which comprises coiling a wire into a plurality of coils of substantially the same diameter and bending back a portion of said coils to intersperse another portion of said coils.

2. The method of making an electric heater for thermionic tubes which comprises coiling a wire into a plurality of coils of substantially the same diameter, bendingA back a portion of said coils to intersperse another portion of said coils, and coating said wire with an insulating coating.

3. The method of making an electric heater for vacuum tubes which comprises coiling a Wire into a plurality of coils of substantially the same diameter, bending back a portion of said coils to intersperse another portion of said coils and coating said heater with an insulating and stiffening substance.

WILLIAM J KIMMELL.

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